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Go Back   SailNet Community > On Board > Gear & Maintenance > Battery Charging . . . again !!
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Thread: Battery Charging . . . again !! Reply to Thread
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Topic Review (Newest First)
09-09-2008 09:16 PM
SYMandalay
Quote:
Originally Posted by MrSeaDragon View Post

Questions : Regardless of how my batteries are combined the alternator will at some point be charging 1 almost full battery and 1 almost empty battery bank, so what charge level (voltage?) does it use to determine its output ?
If there is one voltage regulator for both batteries the charging device will see a voltage that is a combination of the two battery voltages. If both batteries were the same size, the voltage would be close to the average of the two batteries, but if one is a lot larger than the other, then its voltage will overwhelm the other to some degree. A large house batt at 11 volts and a small starting batt at 12.6 volts might result in a combined voltage of (guessing) 11.5 volts. This means the charger will pump out close to its maximum......but most of the current will flow into the house batt that needs it.

Bottom line.....don't worry about it, except in the case where you do not charge for very long and the starting battery has the potential to give up some of its charge to the house bank.
09-09-2008 02:46 PM
Maine Sail
Quote:
Originally Posted by RAGTIMEDON View Post
the way you describe it you could not set both battery banks to ON.
Yes that is what I want to do but in in one switch a 1/2/OFF but I can't find one.


Quote:
Originally Posted by RAGTIMEDON View Post
But normally both are on momentarily as you change the switch, I believe, in order to protect the diodes in your regulator, which fry very rapidly if both batteries are disconnected during the switching process. Isn't that true?
Yes the 1 to 2 contact plates on a 1/2/OFF switch would need to be make before break when moving from position 1 to position 2. I just want a switch with no option for leaving it set in the "both" position. Though in my situation where I have my alt wired directly to my load or house bank there is no way I can fry my diodes or disconnect the load from the alt.

I will probably wind up wiring in two switches with one hidden inside the battery compartment....

I have a toddler and a simple on/off is probably safer anyway. I'd love to find one that could lock "on" but that would not meet "emergency disconnect" standards for ABYC so it will clearly never be made even though I have fuses within 6" of my battery posts. They only make them to lock in the OFF position..
09-09-2008 02:29 PM
RAGTIMEDON Halekai - I once chartered a Bendytoy with two on - off switches attached to two battery banks. Seemed like a sensible thing, so I wired my boat with one on-off to the house bank (4 27's) which stays on and one to the starting battery which is hidden and nearly always off. The start battery is charged by the house bank via an echo-charger, but could be charged by my shore power charger or by my alternator if I closed that switch. To get both, I need to set both switches to ON. I know that is not quite what you wanted - the way you describe it you could not set both battery banks to ON. But normally both are on momentarily as you change the switch, I believe, in order to protect the diodes in your regulator, which fry very rapidly if both batteries are disconnected during the switching process. Isn't that true?
09-09-2008 01:06 PM
Maine Sail
Sure.

Quote:
Originally Posted by hanarg View Post
Hi All

I'm interested in the echo charger since it seems like an elegant solution to the whole issue. However in our boat the engine has only two wires, ground and positive. The positive provides a charge for starting and the alternator sends its charge down that same wire back to the battery. In this case it seems impossible to charge on the house bank side. Is there any way to work around this?

thanks.

Sure there is an easy way;

1) Remove the positive jumper wire from the alt output post that jumps over to the large positive stud on the starter. This is most likely how it's wired.

2) Replace this short jumper wire with a longer one that goes directly from the alt output post to the house bank and does not go through the starter wire. Be sure to fuse this wire within 6" - 10" of the battery.


3) Don't forget to size this wire to carry the amperage the distance you need.


By doing this re-wire you can no longer fry your diodes by switching the battery switch through off while the engine is running because the alt is always connected to the load or house bank.

Once the Echo senses a charge voltage it would then begin to charge the start bank. By wiring this way you can still start on your start/emergency or your house bank which ever you choose.

I really wish I could find a 1/2/OFF switch with NO both setting!!!!!
09-09-2008 12:44 PM
hanarg Hi All

I'm interested in the echo charger since it seems like an elegant solution to the whole issue. However in our boat the engine has only two wires, ground and positive. The positive provides a charge for starting and the alternator sends its charge down that same wire back to the battery. In this case it seems impossible to charge on the house bank side. Is there any way to work around this?

thanks.
09-07-2008 10:23 PM
davidpm
Quote:
Originally Posted by btrayfors View Post
They also facilitate the simplification of your onboard power setup. You simply route all onboard charging devices -- alternator, generator, battery charger, solar panels, wind generator, etc. -- to the house battery bank.

So, you have:

1. a house battery bank (one large bank) charged by whatever means; and
2. a starting battery kept charged by an EchoCharge or DuoCharge device.

Simple, not expensive, and very effective. Your batteries will love you for it :-)

Bill

How do you start the engine if the start battery is dead for some reason.
Some kind of crossover switch. How is it wired and what switch is used?

Assuming 1 is start and 2 is house do you just keep your existing 1,2,all switch set at the 2 position and forget about it unless the something catastrophic happens to 1 and then switch to 2 to start.
Oh and set the alternator to charge 2 only.
07-11-2008 09:02 PM
btrayfors
Quote:
Originally Posted by halekai36 View Post
When batteries are combined they self equalize fairly quickly. The alt sees one bank at the new charge level after combining..

For example if you had a half charged house bank and combine did with a 100% start battery the start battery would fill the house bank until they were both at the same voltage..
Exactly! Which is why I don't like battery combiners.

A much better solution, IMHO, is the newish breed of devices specifically designed to keep a second battery charged, without combining the two banks.

The Xantrex EchoCharge and the Balmar DuoCharge are two such devices. These work by sensing a charging voltage on the house bank and, when present, they bleed off some of the charging current as needed to charge a second battery or battery bank. The EchoCharge has a maximum capacity of 15A, and is perfect for maintaining a starting battery, which doesn't require much charging at all. The DuoCharge is somewhat more sophisticated, and expensive, and can handle up to 30A.

I've had an EchoCharge for several years on my boat, and have installed several DuoCharges on customer's boats. They work beautifully.

They also facilitate the simplification of your onboard power setup. You simply route all onboard charging devices -- alternator, generator, battery charger, solar panels, wind generator, etc. -- to the house battery bank.

So, you have:

1. a house battery bank (one large bank) charged by whatever means; and
2. a starting battery kept charged by an EchoCharge or DuoCharge device.

Simple, not expensive, and very effective. Your batteries will love you for it :-)

Bill
07-11-2008 08:19 PM
Maine Sail
Quote:
Originally Posted by MrSeaDragon View Post

Questions : Regardless of how my batteries are combined the alternator will at some point be charging 1 almost full battery and 1 almost empty battery bank, so what charge level (voltage?) does it use to determine its output ?

Kind regards,
Greg.
When batteries are combined they self equalize fairly quickly. The alt sees one bank at the new charge level after combining..

For example if you had a half charged house bank and combine did with a 100% start battery the start battery would fill the house bank until they were both at the same voltage..
07-11-2008 04:34 PM
sailingdog The current from the alternator will go to both batteries, since the ACR combines the two banks. However, the house bank, being at a lower charge level would have a much lower internal resistance, so the bulk of the current would end up going to the house bank. As the house batteries charge, the internal resistance will increase, as will the voltage the batteries are at.

As to voltage levels... that really depends more on the voltage regulation system you have installed and what kind of charger you have. Ideally, the charging source should be connected to the side that has the greater load, generally the house battery bank. Yes, both banks will be charging at the same voltage level.

However, to prevent a dead battery bank—not low, but dead—from depleting the other battery bank, the ACR will NOT combine the banks if one bank shows a voltage of less than 10.8 VDC. Given that a 12VDC battery system at 0% charge is 11.4-11.6 VDC or so, this is a pretty reasonable limitation.

Yes, in theory, you could discharge the starting bank into the house bank, but it would require you to be doing some unusual things. Like starting the engine, running it for a very short time period and then shutting it off repeatedly with the house bank nearly dead. If you did manage to run your house bank down to say 11.0 VDC, it would become a drain on the starting battery whenever the battery combiner kicked in. If you then decided it was smart to start and stop your engine repeatedly under these conditions, you'd basically get what you deserve IMHO. However, in most cases, that kind of idiotic behavior is going to kill the starting battery to begin with, and it certainly isn't good for the engine either.

BTW, since you're generally not supposed to run batteries down much below 50% on a properly designed DC electrical system, the scenario you're describing is one that shouldn't occur except in unusual circumstances. If you find you're constantly running the house battery bank down to less than 12.0 VDC, you really need to either lower your usage or increase your house battery bank size.

Quote:
Originally Posted by denverd0n View Post
This is where I get confused about what, exactly, the ACR does. Let's say the house bank is nearly dead. The starting battery, on the other hand, is fully charged. You start up the engine. So far so good. Now what does it do?

The starting battery has only had a small amount of energy drawn from it and only needs a bit of charging. The house bank, on the other hand, is near dead and needs a lot of charging. A fairly high charging voltage is needed for the house bank at this time, but only a pretty low one for the starting battery. Do they both get the same voltage? Does the ACR actually combine both so that the starting battery discharges into the house bank? And then they both get charged back up together?

What if, for some reason, you only want to motor for a short while at this point, and would rather charge your house bank later? If the starting battery has been discharged into the house bank, unless you run long enough to fully charge everything, then you may have trouble starting the next time!

If you're going to be stupid about the way you use your boat, no piece of equipment in the world is going to be able to prevent you from killing your batteries.

Is this right? Or am I missing something?

Thanks!
07-11-2008 04:13 PM
GBurton It probably closes when it detects the high voltage from the alternater....ohms law dictates that the battery with the lower voltage will get the most current
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